Hermetically sealed compression loaded bipolar transistor packages are known. FIG. 1 illustrates a commercial package of a disk-shaped compression loaded bipolar power transistor 12 which contains a thick metallic disk 14 which is electrically connected to the emitter region of the bipolar transistor through a molybdenum washer 16 which contacts the emitter region throughout the bottom surface of the transistor. The thick metallic disk 14 functions as an electrical contact and heat sink for the emitter. The thick metallic disk 14 contains a central aperture 18 and a radial projecting slot 20 extending from the central aperture to the exterior of the disk. Within the aperture 18 is an insulator 22 which contains a base contact 24. An electrical lead 26 extends from the base contact 24 through the slot outward through an annular ceramic member 28. Electrically conductive metallic top and bottom covers 30 and 32, respectively, are brazed to the top and bottom of the annular ceramic member. This construction, while operating satisfactorily as a high power transistor switch, has a number of disadvantages. First, the height of the annular ceramic member 28, which is necessary to provide sufficient electrical insulation to avoid electrical conduction between the base lead 26 and the top and bottom covers 30 and 32 to maintain proper electrical operation of the device in environments where conductive agents can coat the exterior surface of the ceramic member to cause electrical malfunction or failure of the transistor 12, contributes substantially to the overall height of the package 10. Furthermore, the presence of the thick metallic disk 14 in which the base contact 24 is disposed contributes substantially to the overall height and weight of the package 10.
Compression loaded bipolar transistor switches are also known which establish contact with the base on only the outer rim of the surface which contains the emitter.
In applications such as converters and inverters, a plurality of hermetically sealed transistor switches are stacked and compression loaded to complete electrical connections. Therefore, individual high profile hermetically sealed bipolar transistor switches are disadvantageous from a spatial consideration in that the height of the overall compression loaded stack is increased. Furthermore, the weight of the overall compression loaded stack is increased as a consequence of the aforementioned thick metallic disk 14.
Since high power bipolar transistor switches in converters and inverters have applications in airframes for use in variable speed constant frequency power generating systems (VSCF), any increased height in the profile of a hermetically sealed high power transistor switch and increased weight is disadvantageous given the premium of space in airframes and the disadvantage of increased weight in the overall operational efficiency of the airframe.
Semiconductor packages are disclosed in U.S. Pat. Nos. 3,536,966; 3,931,635; 4,188,637; 4,710,795 and Swiss Patent No. 434,482. U.S. Pat. No. 3,931,635 discloses a semiconductor device in which a control electrode of the semiconductor device extends through insulative rings. The use of an insulator in the sides of the power semiconductor device creates a high profile in which the height of the insulator substantially contributes to the overall height and weight of the semiconductor device which is disadvantageous in applications where weight and space are critical, such as airframes. FIGS. 11-13 of Swiss Patent No. 434,482 disclose a compression loaded controllable rectifier having identical cover lids 70 and 71 which are joined to ceramic rings 68 and 69. The ceramic rings have the disadvantage that they increase the thickness and weight of the semiconductor device. U.S. Pat. No. 3,536,966 discloses a semiconductor device having an annular insulator ring 26 through which extends a lead 14 of a control electrode. The annular insulator ring 26 adds to the overall height and weight of the semiconductor device.